Stabilizing device for a transmission line-mounted surge arrester

ABSTRACT

A line arrester, which is articulately suspended from a transmission or distribution network and on which a stabilizing device is arranged. The stabilizing device increases the mass-moment of inertia of the line arrester so as to contract movements of the line arrester deviating from the vertical line. The stabilizing device has a mass center which substantially conforms to a vertical line which passes through the mass center of the line arrester.

TECHNICAL FIELD

The present invention relates to a transmission line-mounted surgearrester (hereinafter referred to as line arrester) with a stabilizingdevice for use in air-insulated power transmission lines in high-voltagetransmission or distribution networks, that is, in electric networkswith voltages from a few kilovolts up to several hundred kilovolts. Thepresent invention also relates to a method in and use of such astabilizing device.

BACKGROUND ART

Line arresters exhibit a non-linear current-voltage characteristic inthat their conductivity increases non-linearly with the voltage. Modernline arresters comprise series-connected blocks of substantially zincoxide which are enclosed in a porcelain or polymer insulator. At normalvoltages across the blocks, their conductivity is practically zero, butat high voltages the blocks become electrically conductive. To preventovervoltages, such as switching overvoltages or overvoltages caused bylightning strokes, from propagating in air-insulated transmission lines,line arresters are connected, at regular intervals, to the conductors ofthe transmission line. If over-voltages reach switchgear, they maydamage electrical apparatuses or force circuit breakers to trip, thusdestroying large parts of the electric network.

Line arresters have an elongated shape and are electrically connected atone of their ends to one of the conductors of the transmission line andat their other end to ground potential. In a commonly occurring mountingarrangement, the line arrester is articulately suspended from a point ofattachment on the transmission line. The line arrester is suspendedvertically in the transmission line and is connected, at its lower end,to ground, normally via a conducting wire, so-called slack. In thefollowing, line arrester means a line arrester which is articulatelysuspended from an attachment point of a transmission line. According tothis mounting arrangement, the line arrester, while being influenced byexternal forces from, for example, wind or earthquakes, may be broughtto oscillate or swing, the longitudinal axis of the line arrester thusbeing forced to deviate from the vertical line. Due to this deviationfrom the vertical line, there is a risk that the phase-to-phase andphase-to-ground distance for the transmission line falls below theprescribed smallest distance.

SUMMARY OF THE INVENTION

A first object of the presents invention is to provide a stabilizingdevice for a line arrester, articulately suspended from an attachmentpoint of a transmission line, by means of which the above-mentionedproblems with deviation from the vertical line may be reduced.

A second object of the present invention is to provide a method in astabilizing device for a line arrester, articulately suspended from anattachment point of a transmission line, by means of which theabove-mentioned problems with deviation from the vertical line may bereduced.

The first object according to the above is achieved by arranging atleast one stabilizing device at the line arrester by means of which themass-moment of inertia of the line arrester is increased. In order toretain the orientation of the line arrester in the vertical line, themass centre of the stabilizing device shall substantially conform to thevertical line which passes through the mass centre of the line arrester.

When a line arrester is subjected to a wind load, the wind influencesthe line arrester with a torque which strives to rotate the linearrester from the vertical line. To counteract this torque, at least onestabilizing device is arranged at the line arrester and by adapting themass of the stabilizing device, the geometrical shape and/or location ofthe stabilizing device at the line arrester, the mass-moment of inertiaof the line arrester may be adapted to the external forces which areexpected to influence the line arrester. The expected forces then dependon the location where the line arrester is mounted; for example, strongwinds may be expected along coasts and in valleys. With knowledge ofthis, the mass-moment of inertia of the line arrester may be adaptedsuch that the longitudinal axis of the line arrester does not deviatefrom the vertical line by more than a given maximum angle. In mostcases, the maximum angle may be allowed to be 15° without thephase-to-phase and phase-to-ground distance falling below the prescribedminimum distance.

The mass of the stabilizing devices, the shape and/or location of thestabilizing devices at the line arrester may also be adapted to the typeof line arrester at which the stabilizing device is arranged. Forexample, line arresters of various sizes may be caused to have the samemass-moment of inertia by individual adaptation of the stabilizingdevice of the respective line arrester.

According to a preferred embodiment of the invention, the stabilizingdevice comprises a weight which is attached to the lower end of the linearrester. By dimensioning the mass of the weight, the mass-moment ofinertia of the line arrester may be adapted to the external forces whichare expected to influence the line arrester. A weight with a large massgives a greater mass-moment of inertia than a weight with a small massand the resistance of the line arrester to deviate from the verticalline thus increases. By arranging the weight at the line arrester suchthat the mass centre of the weight substantially conforms to thevertical line which passes through the mass centre of the line arrester,the orientation of the line arrester in the vertical line is retainedalso when no wind load occurs.

By arranging the stabilizing device at the line arrester, the naturalfrequency of the line arrester is changed. This can be made use of forincreasing the capacity of the line arrester to resist periodicallyrecurring gusts of wind of a certain frequency. The line arrester isthen arranged with at least one stabilizing device with which themass-moment of inertia of the line arrester is adapted such that thenatural frequency of the line arrester is brought to deviate from thefrequency of the periodically recurring gusts of wind.

The second object according to the above is achieved by arranging theline arrester with at least one stabilizing device which increases themass-moment of inertia of the line arrester.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail in the following withreference to the accompanying figures, wherein

FIG. 1 shows a preferred embodiment of a stabilizing device in the formof a weight arranged on a line arrester, and

FIG. 2 shows a detailed view of the stabilizing device shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a line arrester 1 which is articulately suspended from apoint of attachment 2 on a transmission line 3. The line arrester 1 isthus hanging perpendicularly in the transmission line 3 when it is notinfluenced by any external force. Corona rings 4 are arranged at theline arrester 1 to prevent partial discharges (corona) in the air aroundthe line arrester 1. At the lower end of the line arrester 1, astabilizing device 5 in the form of a weight is arranged. By suitablydimensioning the mass of the weight 5, the mass-moment of inertia of theline arrester 1 may be adapted to the external forces which are expectedto influence the line arrester at the location where the line arresteris to be installed. The weight is arranged such that its mass centresubstantially conforms to the vertical line which passes through themass centre of the line arrester. In this way, the line arrester retainsits orientation in the vertical line also when no external force, forexample wind load, occurs

FIG. 2 shows a detailed view of the weight 5. In the figure, the weight5 is articulately arranged at the line arrester 1 by means of a joint 6which is movable in a plane. The joint 6 permits a suitable weight 5 tobe easily arranged at the line arrester 1.

In FIGS. 1 and 2, only one stabilizing device 5 is arranged at the linearrester 1. It is to be understood, however, that the scope of theinvention, in addition to what is described above, allows for numerousdifferent ways of arranging one or a plurality of stabilizing devices ina line arrester for the purpose of changing the mass-moment of inertiathereof.

What is claimed is:
 1. A line arrester comprising a first end, in whichis arranged an attachment point which allows the line arrester anoscillating movement, and a second end which is capable of swingingfreely, wherein the line arrester in the second end comprises astabilizing device which, when being externally influenced, counteractsa deviation of the line arrester from a vertical line.
 2. A linearrester according to claim 1, wherein the stabilizing device comprisesat least one weight.
 3. A line arrester according to claim 1, whereinthe stabilizing device is articulately attached to the line arrester. 4.A line arrester according to claim 2, wherein the stabilizing device isarticulately attached to the line arrester.
 5. A line arrester,articulately suspended from an attachment point of a transmission line,wherein the line arrester comprises a stabilizing device which isadapted to increase a mass-moment of inertia of the line arrester and tocounteract a deflecting movement of the line arrester from a verticalline, caused by external stress, which stabilizing device has a masscenter which substantially conforms to the vertical line which passesthrough the mass center of the line arrester.
 6. A method in a linearrester comprising a first end, in which is arranged an attachmentpoint which allows the line arrester an oscillating movement, and asecond end which is capable of swinging freely, in order to stabilizethe line arrester and to counteract oscillations in case of externalinfluence, wherein the second end of the line arrester is brought tocomprise a stabilizing device.
 7. A method according to claim 5, whereinthe stabilizing device is brought to comprise a weight.
 8. A method in aline arrester, which is articulately suspended from an attachment pointof a transmission line, for counteracting a movement deviating from avertical line, wherein the line arrester is adapted to comprise astabilizing device, whereby a mass-moment of inertia of the linearrester is increased, and whereby a mass center is imparted to thestabilizing device, which mass center substantially conforms to thevertical line which passes through the mass center of the line arrester.9. Use of a line arrester according to claim 1, in one of a transmissionnetwork and a distribution network.
 10. Use of a line arrester accordingto claim 2, in one of a transmission network and a distribution network.11. Use of a line arrester according to claim 3, in one of atransmission network and a distribution network.
 12. Use of a linearrester according to claim 4, in one of a transmission network and adistribution network.
 13. Use of a line arrester according to claim 5,in one of a transmission network and a distribution network.
 14. Use ofa line arrester according to claim 6, in one of a transmission networkand a distribution network.
 15. Use of a line arrester according toclaim 7, in one of a transmission network and a distribution network.16. Use of a line arrester according to claim 8, in one of atransmission network and a distribution network.